Silencing and indicating device



Aug. 6, 1940.`

M. C. JONES SILENCING AND INDICATING DEVICE Filed July 30, 1938 y Bg attorney Patented Aug. 6, 1940 UNITED Y, STATESv SILENCING 'AND INDICATING DEVICEy Mack C. Jones, Haddon HeightsfN. J., assignor to Radio Corporation of America, a corporation of Delaware Application July so, 193s, serial No. 222,108

Ihis vinvention relates to silencing and indicating devices such as are useful for indicating the tuning of radio apparatus and for silencing such apparatus during periods of Zero orlow signal level. It has for its principal object the provision o-f a combined tuning indicator and silencer which is inexpensive, is of simple construction, and is readily applicable to different types of apparatus. 4 y

1U A distinguishing Characteristic of the herein disclosed embodiment of the invention is the use of a tuning indicator electron discharge device, such as that disclosed by United States Patents 2,051,189 and. 2,094,684, both to indicate the tuning of a radio receiver and to silence the receiver when the received signal level is below a predetermined value.

The invention will be better understood from the following description consideredv in connection with the .accompanying drawing, and its scope is indicated by the appended claims.

The single figure of the drawing is a wiring diagram illustrating the application of the invention to a radio receiver. It should be understood, however, that this showing is merely illustrative of one of the many possible embodiments of the invention.

The illustrated circuit includes modulated carrier supply means, shown as a lead lil which is 30 coupled through a transformer II to a modulation or audio frequency detector l2, the primary and secondary circuits. of the transformer I I being tuned, respectively, by the capacitors I3 and I4, and the detected output being derived from 35 the resistors I5 and I6.

From the terminal l1 of the resistor I5 there is derived an automatic volume control potential which is applied, through a filter network including a resistor I8 and a capacitor I8', to preceding ampliier stages (not shown), as is customary in circuits of this character.

From the adjustable volume control terminal (ol. o-2o) v plied through the lower lead vof the bloede resistor section 3 I. f

Tuning of the channel including the detector I2 and the amplifier 22 is indicated by an electron discharge device 32, which may be of the. same type as that disclosed by the aforesaid patents. This visual indicating device 32 includes a twosection cathode 33, an amplifier grid 34 and an amplier anode 35 surroundingA one section ofl the cathode, and a visual indicator 36 and a control 10 electrode 31 which surrounds the other section of the cathode. As will be apparent, the anode 35 is connected to the control electrode 31 of the visual indicating element of the device, and the pattern onr the indicating element or target 36 is determined by the value of the current -flowing through a resistor 38 connected between the amplifier anode35 and the indicating device fluorescent anode or target 36. Potential is applied to the amplier control grid 34 of the device 32 20 through the lead I1, and a filter network including a resisto-r 39 and a capacitor 4i) and anodecathode potential is applied through the plus B lead and one of the ground leads 23.

when the channel Iva- 22 is detuned, the enr- 25 rent through the resistors l5 and I6 is low, the potential of the indicator device control grid 34 approaches that of the detector and indicator device cathodes, a relatively large current flows I through the resistor 38,l the amplifler anode 35 '50 and indicator control electrode 31 become negative withv respect to the constant voltage fluorescent target 36, and there is produced on this target a shadow the size of which is determined by the resistor 38 and the constants of the various 35 circuits. f

When the channel I2-22 is tuned to resonance, the current of the resistors I5-I 6 is a maximum, the grid 34 is more negative with respect to the cathode 33, the current of the anode 35 is re- 40 duced, the target 36 and the control electrode 31 approach the same voltage, electrons reach more of the surface of the target 36, which then exhibits a luminous glow over its entire surface,

amplifier 22, and there is interposed between the lead 30 and the common lead 43 of the resistors 55 4| and 42 a diode which is shunted by a. capacir tor 45.

With these connections, the indicating device anode 35, the grid of the amplifier 22, and the anode of the diode 44 approach cathode or ground potential during periods of low signal, and the amplier and diode circuits are interrupted. As the signal level increases, the indicating device grid becomes more negative, less current flows through the resistor 38, and the potential of the indicator and diode anodes and of the amplifier control grid becomes more positive, thus permitting the signal to pass through the amplifier 22. The bias potential applied to the amplifier grid 2| through the resistor section 3| is set by the diode 44, which maintains zero voltage between its cathode and anode when the anode tends to go positive due to the decreased drop of the resistor 38. The signal level at which the amplier 22 begins to pass the signal is, of course, determined by the voltage applied to the lead 30, which obviously may be adjusted along the bleeder resistor 2S if desired.

Otherwise stated, the device 32, which heretofore has served merely as a visual tuning indicator, now also functions during periods of low signal level to apply to the amplifier 22 a control grid bias whereby the signal is interrupted, and during periods of high signal level to permit the application of normal bias potential to this grid from the bleeder resistor 29.

I claim as my invention:

l. The combination with a radio signal rectifier and a signal amplifier coupled to said rectier, of a signal-responsive indicator tube having a control grid and an anode, means for applying a bias potential to said control grid, means in circuit with said anode providing a variable potential thereon in response to variations in potential on said control grid, means providing a connection between said anode and the amplifier to provide normal operation of said ampliiier,

a potential drop producing resistor in said lastnamed connection, a diode rectier device having an anode electrode connected with the output end of said potential drop producing device and having a cathode, means providing a xedsource of biasing potential for said amplifier of a value to effect substantially cut-off of the signal flow through said amplifier, said last-named means providing a negative terminal connected with the diode cathode and a circuit interconnecting said amplifier and indicator tube and providing a potential difference between the electrodes of the4 diode such that in the absence of signals the anode is negative with respect to the cathode.

2. In a signal receiving apparatus including a device having a cathode, a control grid, an anode and additional electrodes arranged to indicate Yvisually the tuning of a channel in response to a signal variable biasing potential applied to said control grid, and wherein a` detector is coupled to the input circuit of an amplier, the combination of means including a potential drop producing resistor in circuit with the anode of said indicator device and a connection to the amplifier providing a control circuit responsive to the operation of said device for interrupting the received signal through said amplier during periods of low signal level, means for applying normal grid bias potential to said amplier during periods of higher levels of said signal, a diode rectifier having a cathode connected with said last-named means and having an anode in circuit with said biasing connection for said amplifier and means providing a potential drop through said connection between said anode and the anode of said indicator device.

3. In an apparatus including an electron discharge device having a control grid and an anode, said device being arranged to indicate visually the tuning of a channel wherein a detector is coupled to the input circuit of an amplifier, the combination of means for causing the anode voltage of said device to vary in response to signal variations, means for controlling the grid potential of said amplifier in accordance with the anode voltage variations of said device, and means including a diode connected between the cathode and grid of said amplifier and responsive to a predetermined value of said anode potential for applying normal bias potential to said grid.

4. In a radio signal amplifying channel the combination with a signal rectier providing a signal variable biasing potential, of a signal indicator device comprising a control grid con nected with said signal rectifier, and having an output anode circuit providing a potential variable in response to variations in potential on said grid, a signal amplier having a control grid connected with said anode circuit, a relatively high resistance potential drop producing device in said connection, a diode rectier having an anode connected with the output end of last last-named device and having a cathode, means providing a source of biasing potential for said amplier, and means for applying said biasing potential through said diode rectier device to said amplier in response to variations in potential in said indicator output circuit corresponding to signals of a predetermined high amplitude.

MACK C. JONES. 

